Electromagnetic interference is a common and well-known problem in electronic devices such as radio communication devices. Interfering signals can be capacitively coupled (electrostatic coupling) onto wires in the circuit, magnetically coupled to closed loops in the circuit, or electromagnetically coupled to wires acting as small antennas for electromagnetic radiation. Any of these can become a mechanism for coupling of signals from one part of a circuit to another part of a circuit.
One strategy to reduce interfering signals in a radio communication device is to use an electromagnetic shield. In mobile radio communication devices, the electromagnetic shields usually take the form of a frame that is manufactured from die cast magnesium or metalized injection molded plastic. Electromagnetic shields may also be in the form of a sheet metal can that encloses the printed circuit board. The sheet metal can may be soldered to a printed circuit board, or may be held by spring clips which are soldered to the printed circuit board. In either case the soldering step adds to the expense of manufacturing. Moreover, soldering the can to the printed circuit board makes repairs more difficult.
Lids made of die cast metal or metalized plastic are sometimes used in place of shield cans. Die cast metals and injection molded plastics have a practical limit to the thickness that can be processed, currently about 0.50 mm to 0.80 mm. The practical limit imposed by current technology is one of the limiting factors in designing smaller and lighter mobile phones.
Another problem that is often faced when designing electromagnetic shields for mobile phones is the need to compartmentalize areas on the printed circuit board to isolate circuits from one another. This is usually accomplished by using walls to divide the interior of the shield frame into discrete compartments or by using a plurality of cans. For any given mobile phone, the compartments or cans would be arranged so those components that are likely to interfere with one another are isolated. Different models or types of phones are likely to require different shield geometries to isolate components. This greatly increases cost and time needed for producing new variants of mobile phones. Moreover, since these shields are not interchangeable between various models of phones, there is a need to maintain a relatively large number of shields in inventory.